Patent Document 1 has described a technique in which the full charge capacity of a battery is calculated in performing charge of the battery with an external power source. Specifically, the SOC of the battery is calculated at the start and the end of the charge, and current values detected during the charge are summed to calculate a value (sum value). Then, the difference between the SOCs at the start and the end of the charge and the sum value are used to calculate the full charge capacity of the battery.